All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
If this possessed man is undoubtedly affected by magic— meaning, he does abnormal things that he would not do if he had been in his normal state— then he would not be held responsible for his negligence of prayer. Such a man is considered insane.
However, if this possessed man has the ability to control his actions— meaning, he is able to perform his prayers completely— then he is held responsible and is accountable for his negligence. If he does not perform his prayers until their designated time has elapsed, he would be a sinner. In this case, his prayer will not be accepted if he does not do the required acts of prayer.
And Allaah Knows best.